Support Withdraw 0 trick in L2 ledger

[v0d1ch]

Why

This started as a user request in #1757 and we also think it would be beneficial for our users to be able to re-use the code they write for L1 on L2. It seems that a lot of people are using the withdraw 0 trick to reduce the tx execution costs and simplify the code logic so we should look into this.

What

Keep track of ledger certificates on L2

How

Currently we don't do anything on L2 ledger to maintain the state of registered stake certificates and only keep track of UTxO state

hydra/hydra-node/src/Hydra/Ledger/Cardano.hs

Line 78 in af5c305

, Ledger.lsCertState = def

We could probably keep track of the certificates in the HeadState on L2 (needs grooming) and we should be explicit in our documentation that any certificate state on L2 will not/can't be enforced on L1.